On 10/28/20 4:35 AM, Lukas Bulwahn wrote:
> make clang-analyzer on x86_64 defconfig caught my attention with:
>
> net/sched/cls_api.c:2964:3: warning: Value stored to 'parent' is never read
> [clang-analyzer-deadcode.DeadStores]
> parent = 0;
> ^
>
> net/sched/cls_api.c:2977:4: warning: Value stored to 'parent' is never read
> [clang-analyzer-deadcode.DeadStores]
> parent = q->handle;
> ^
>
> Commit 32a4f5ecd738 ("net: sched: introduce chain object to uapi")
> introduced tc_dump_chain() and this initial implementation already
> contained these unneeded dead stores.
>
> Simplify the code to make clang-analyzer happy.
>
> As compilers will detect these unneeded assignments and optimize this
> anyway, the resulting binary is identical before and after this change.
>
> No functional change. No change in object code.
>
> Signed-off-by: Lukas Bulwahn <lukas.bulwahn@xxxxxxxxx>
> ---
> applies cleanly on current master and next-20201028
>
> Jamal, Cong, Jiri, please ack.
> David, Jakub, please pick this minor non-urgent clean-up patch.
>
> net/sched/cls_api.c | 16 +++-------------
> 1 file changed, 3 insertions(+), 13 deletions(-)
>
> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
> index faeabff283a2..8ce830ca5f92 100644
> --- a/net/sched/cls_api.c
> +++ b/net/sched/cls_api.c
> @@ -2940,7 +2940,6 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb)
> struct tcf_chain *chain;
> long index_start;
> long index;
> - u32 parent;
> int err;
>
> if (nlmsg_len(cb->nlh) < sizeof(*tcm))
> @@ -2955,13 +2954,6 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb)
> block = tcf_block_refcnt_get(net, tcm->tcm_block_index);
> if (!block)
> goto out;
> - /* If we work with block index, q is NULL and parent value
> - * will never be used in the following code. The check
> - * in tcf_fill_node prevents it. However, compiler does not
> - * see that far, so set parent to zero to silence the warning
> - * about parent being uninitialized.
> - */
> - parent = 0;
> } else {
> const struct Qdisc_class_ops *cops;
> struct net_device *dev;
> @@ -2971,13 +2963,11 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb)
> if (!dev)
> return skb->len;
>
> - parent = tcm->tcm_parent;
> - if (!parent) {
> + if (!tcm->tcm_parent)
> q = dev->qdisc;
> - parent = q->handle;
This looks like a an unused error handler.
and the later call to
if (TC_H_MIN(tcm->tcm_parent)
maybe should be
if (TC_H_MIN(parent))
so I am skeptical that this change is ok because the code around it looks buggy.
Tom
> - } else {
> + else
> q = qdisc_lookup(dev, TC_H_MAJ(tcm->tcm_parent));
> - }
> +
> if (!q)
> goto out;
> cops = q->ops->cl_ops;
